As the light of lamps is not sufficiently brilliant and powerful for firework illuminations of this nature, it is necessary to use the burning compounds, such as the zinc light and the antimonial light. The effects may also in this way be varied by adopting different colours, and may be maintained as long as is requisite, by dis posing so many behind the transparency, that one may take fire before the other is quite extinguished.
Of Timeing Fireworks.
Every thing in the compound fireworks, whether burning together or in succession, depends on accuracy in the length of their action, and in the precision with which the various parts begin, end, and follow each other. Even in the simplest, a defect in this respect is very disagreeable to the eye; and, in illuminations, the ornamental appearance is very much injured, unless the lights all expire nearly at the same time. In the same manner, it is absolutely necessary that one work should be completely exhausted before another begins, wherever there are mutations ; and that no interval of darkness should take place between them. All these objects are to be obtained only by great care in the different parts, in the composition, the driving, the lengths of cases, and the priming, the quality, and the fixing of the different leaders, Under the head of compositions, we have already pointed out the way in which these are to be managed for this purpose; so that we need now say nothing more on that subject. In filling, or driving, great care and many attentions are necessary ; as it is here in par ticular that the fireworks are apt to become unequal, and thus to go wrong. The measure by which the composition is to be introduced, should, in the first place, be a cylinder, and not a shovel, as is commonly the case, as it can always he filled more accurately each time; so that the charge to be driven shall be always equal. Each diameter of case should also have its own measure ; and these should all be numbered to corre spond with the moulds, by which means all chances of errors from this cause are avoided. In driving, the same mallet should be used for each size of case, and these should also have corresponding numbers. The workmen should also be careful always to give the sante number of blows; and this being regulated for each class of cases, from sixteen upwards to sixty, the habit of doing it steadily is easily acquired. But in all
larger works, a pile engine, furnished with a tell-tale to keep the account, is the only method to be depended on.
Where there is no such machine, all the cases that are intended to burn together, should, as much as pos sible, be driven by the same individual ; and as the L•bi.1 artist car, number each man's work, he may class the cases accordingly; so as to adopt those, of the length of burning of which he is accurately informed. For all things else, he must depend on such calcula tions as he may choose to make respecting the perform ance of his pieces. But a sample of each kind should be tried, and the time of burning measured by the se cond's pendulum, when it should be marked on each case; that so when the works come to be put together, the operator may be quite sure of what he is doing, and be able to balance and arrange them accordingly. That accurate time is really attainable in this way, is very certain ; because, in military works, out of a thou sand fuses, perhaps, where the time is most important, since the bursting and effect of a shell are entirely regulated by it, it will be found that not a second of dif ference takes place.
With respect to leaders, it is only necessary that they should act as quickly as possible, since no time is allowed for these; and that point is to be ensured by good quick-match, and careful priming and fitting.
Of Sky-Rockets.
We have chosen to treat of kind of firework first, not only on account of its beauty, and its univer sal use in all cases, but, because, in detailing the mi nute attentions which it peculiarly requires, it will be less necessary to dwell on that subject in describing the construction of others. The same precautions and proceedings, in every respect, if in a less degree, are required l'or all sorts of driven cases, whatever their objects may be.
We have, in our table of compositions, given a va riety of those which may be used for sky-rockets, but shall here name that one which is best adapted for those of a pound•wcight, where the original materials, and not mealed powder, are used. This consists of nitre 4 lb., sulphur 1 lb., and charcoal 11 lb. The method of making the cases, and the construction of the moulds i and rammers, having already been described, it is unne cessary to notice them again.